This invention relates to an adaptive engine mount for mounting the engine of a motor vehicle onto the vehicle frame in which the damping characteristics of the engine mount may be changed by operation of an electrically or vacuum actuated control valve.
The dynamic characteristics of a motor vehicle are such that while driving on a smooth road at highway speeds the vehicle may shake and vibrate unless engine mounts having high dynamic stiffness and damping are used to mount the engine on the frame. On the other hand, the engine mounts are required to provide good isolation of the engine during engine idle conditions, which requires a very soft engine mount that has low dynamic stiffness. Accordingly, compromises must be made. As a result, engine mounts are typically designed in which damping is low during low vibratory inputs and in which higher damping and resulting stiffness is provided during higher vibratory input conditions.
However, vehicle operating conditions exist when the higher dynamic stiffness and damping are desirable even though the vibratory inputs may be relatively small. Accordingly, it has been disclosed in U.S. Pat. No. 5,205,546 to provide a solenoid actuator in a dynamic engine mount which can switch the mount to the higher stiffness mode at any driving condition.
The present invention provides a dynamic engine mount in which stiffness and damping can be changed to accommodate varying driving conditions This is achieved by providing a control cavity in the fixed wall separating the pumping chamber and reservoir of a conventional engine mount. The wall includes an orifice track through which fluid is pumped to achieve the higher stiffness and damping. A decoupling diaphragm is mounted in the wall, one side of which is exposed to the fluid in the pumping chamber, and the other side of which is exposed to the pressure level in the control cavity. During normal operation, the control cavity is vented to atmosphere, and the mount functions as a typical hydraulic mount; that is, the mount provides low dynamic stiffness and damping for small vibratory inputs and higher dynamic stiffness and damping for larger vibratory inputs. However, a solenoid actuator may by actuated for any vibratory input to trap air in the control cavity, which acts as an air spring resisting movement of the decoupling diaphragm, thereby increasing damping for any vibratory input.